Plasma processing apparatus

ABSTRACT

In a microwave plasma processing apparatus, a metal made lattice-like shower plate  111  is provided between a dielectric material shower plate  103 , and a plasma excitation gas mainly an inert gas and a process gas are discharged form different locations. High energy ions can be incident on a surface of the substrate  114  by grounding the lattice-like shower plate. The thickness of each of the dielectric material separation wall  102  and the dielectric material at a microwave introducing part is optimized so as to maximize the plasma excitation efficiency, and, at the same time, the distance between the slot antenna  110  and the dielectric material separation wall  102  and a thickness of the dielectric material shower plate  103  are optimized so as to be capable of supplying a microwave having a large power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 10/861,388, filed Jun. 7, 2004, now U.S. Pat. No. 7,520,245, whichis a continuation of U.S. application Ser. No. 09/678,741, filed Oct. 4,2000, now U.S. Pat. No. 6,830,652, which is a continuation ofPCT/JP00/03365, filed May 25, 2000 and for which priority is claimedunder 35 U.S.C. §120. This application is based upon and claims thebenefit of priority under 35 U.S.C. § 119 from the prior Japanese PatentApplication No. 11-186258, filed May 26, 1999, the entire contents ofall applications are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to plasma processing apparatuses and, moreparticularly, to a plasma processing apparatus which is capable ofperforming a high performance plasma process and has a highelectric-power-efficiency and a long maintenance period.

BACKGROUND ART

In recent years, in order to realize semiconductors and liquid crystaldisplays having a high-performance and high-throughput, a plasma processhas become indispensable for manufacturing these products. Althoughthere are various methods for plasma excitation, a parallel plate typeRF plasma excitation apparatus or a inductive coupling type plasmaapparatus has been used to manufacture semiconductors or liquid crystaldisplays. These plasma apparatuses have several essential problems inthat a large damage is given to a device and a high-performance processat a high-speed cannot be achieved. Accordingly, it has become difficultto satisfy demands of semiconductors and liquid crystal displays to havea high-performance and high-throughput

Accordingly, a microwave plasma apparatus has recently been attractingattention, which can excite high-density plasma by a microwave electricfield without using a direct current magnetic field. As such kind ofmicro plasma apparatus, an apparatus (Japanese Laid-Open PatentApplication No. 9-63793) is known, which excites plasma by ionizing agas in a vacuum chamber by a microwave electric field generated by amicrowave emitted to the vacuum chamber from a flat antenna (slotantenna) having many slots that are arranged to generate a uniformmicrowave. Additionally, there is also known an apparatus (WO98/33362),which excites plasma by introducing a microwave, which is emitted by aslot antenna provided outside a vacuum chamber, into the vacuum chamberby being passed through a dielectric material separation wall and adielectric material shower plate. Since the microwave plasma excited bythose methods has a high-density and a low electron temperature, aprocess having no damage at a high speed can be performed. Additionally,since uniform plasma can be excited even on a large area substrate, itcan be easily dealt with an increase in the size of a semiconductorsubstrate or a liquid crystal display.

However, these conventional microwave plasma apparatuses have a problemin that a substance, which is produced by dissociation and combinationof a process gas due to the plasma, adheres onto a surface of thedielectric material separation wall or the shower plate. If a filmhaving a low resistivity is deposited on the surface, the microwave isreflected, and if a film having a high resistivity, the microwave isabsorbed. Accordingly, the plasma excitation power is decreased due toadhesion of the substance onto the surface of the dielectric materialseparation wall or the dielectric material shower plate, which reducesthe plasma density and deteriorates stability of the plasma. In theworst case, it becomes a situation in which the plasma cannot be exited.In order to eliminate such a problem, it is necessary to frequentlyperform a chamber cleaning and maintenance so as to remove the adheredfilm, which significantly decreases the throughput.

In the reactive ion etching which is indispensable for producingsemiconductors or liquid crystal displays, anisotropic etching isachieved by irradiating ions in the plasma onto a substrate surface byaccelerating up to 100 eV by an electric filed in a sheath formedbetween the substrate and the plasma. In order to generate a directcurrent voltage (self bias voltage) for accelerating the ions to adesired energy in the sheath near the substrate, an RF wave ranging fromabout several hundreds KHz to about several tens MHz is applied to thesubstrate. Since the plasma can be regarded as a conductive material,the RF voltage applied to the substrate is divided into that the sheathnear the substrate and the sheath near the grounded part. That is, ifthe RF wave is applied to the substrate, the RF voltage is applied notonly to the sheath near the substrate but also to the sheath near thegrounded part, and, thereby, the DC voltage of the sheath near thegrounded part is increased and a plasma potential is increased. If theplasma potential becomes greater than 15 to 30 V, contamination occursdue to sputtering of the surface of the grounded part due to bombardmentof the accelerated ions.

A ratio of the RF voltages applied to the sheath near the substrate andthe sheath near the grounded part is determined by impedances of thesesheathes. If the impedance of the sheath near the grounded part is muchsmaller than the impedance of the sheath near the substrate, a most partof the RF voltage applied to the substrate is applied to the sheath nearthe substrate. That is, if the area of the grounded part to which theplasma contacts is sufficiently larger than the area of the substrateelectrode (normally, more than four times), the plasma potential is notincreased when a RF wave is applied to the substrate. Thus, a problemassociated with the contamination due to the sputtering can be avoided.Additionally, a large DC voltage can be efficiently generated in thesheath near the substrate.

However, in the conventional microwave plasma apparatus, since theopposing surface of the substrate is covered by a dielectric material inits entirety, the area of the grounded part to which the plasma contactscannot be large. Normally, an area of the grounded part to which theplasma contacts is less than about three times the area of the substrateelectrode. Accordingly, it is difficult to apply to an reactive ionetching such as a process in which a high energy ions must be bombardedto a substrate surface.

In a process for forming a thin film containing a metal such as metalthin film, feroelectric film, and high dielectric thin film by CVD(chemical vapor deposition) method, and an organometallic gas which is acompound of metal atoms and organic molecules is used. If the bondsbetween the metal atoms and the organic molecules is selectively cutoff, a thin film having a good characteristic which causes no impuritycontamination will be formed. However, if the organic molecules aredecomposed, a large amount of carbon impurity atoms are mixed into thefilm, which deteriorates the characteristic of the thin film.Additionally, in the etching process, if the dissociation of the processgas progresses in excess, the selectivity between the film to be etchedand a resist mask or the underlying material is deteriorated, and itbecomes difficult to etch a fine pattern having a large aspect ratio. Inthe conventional microwave plasma processing apparatus, the process gasis directly introduced into an area close to a position at which themicrowave is incident and having a high plasma density and a relativelyhigh electron temperature. Thereby, the dissociation of the process gasprogresses in excess, and a good result cannot be obtained in formationof a thin film using an organometallic gas or fine pattern etching.

When a microwave is incident on plasma, the microwave propagates in theplasma if the electron density if smaller than the cutoff density n_(c)represented by the following equation.

n _(c)=∈₀ω² m ₀ /e ²

where ∈₀ is a permittivity of dielectric ratio of vacuum; ω is microwaveangular frequency, m₀ is a mass of an electron, and e is a charge of anelectron. On the other hand, if the electron density is higher than thecutoff density, the microwave is reflected in the vicinity of a plasmasurface. At this time, the microwave penetrates into the plasma by apenetration length (normally, several millimeters to ten millimeters),and gives energy to electrons in the plasma so that the plasma ismaintained. In to the microwave plasma excitation, if the electrondensity is lower than the cutoff density, uniform and stable plasmacannot be excited due to dispersion of the microwave in the chamber. Inorder to excite uniform and stable plasma, it is indispensable toreflect a large part of the microwave by exciting plasma having anelectron density sufficiently higher than the cutoff density in thevicinity of the surface on which the microwave is incident. In order toexcite a stable plasma having a high electron density, an inert gas suchas Ar is preferably used as the plasma excitation gas. If a gas otherthan a monatomic molecule gas is added, it tends to deteriorate thestability of the plasma due to the electron density being decreasedsince the energy of the microwave is used for dissociation of the gasmolecules. In the conventional microwave plasma apparatus, since only asmall amount (several percent) of gas other than the inert gas can beadded, there is a problem in that process window is narrow and it cannotdeal with a high speed process.

When the electron density in the vicinity of the plasma surface ishigher than the cutoff density, a large part of the microwave incidenton the plasma is reflected in the vicinity of the surface. The reflectedwave is received by the slot antenna, and, thereafter, emitted from theslot antenna by being reflected by a matching unit connected between theslot antenna and the microwave power source. The microwave graduallyprovides its energy to the plasma while repeatedly reflected between theplasma surface and the matching unit. That is, the microwave is in aresonant state in a part between the plasma surface and the matchingunit. Accordingly, a high energy density microwave is present in thispart, and a large loss is caused due to a small conductive loss of ametal wall of the waveguide or a small dielectric loss of the dielectricmaterial. In the conventional microwave plasma apparatus, these lossesare large, and, thereby, the plasma excitation power efficiency was low.Additionally, if a large power microwave is supplied so as to obtain ahigh-density plasma, an arc discharge is generated in a slot part formedon the surface of the slot antenna. Thereby, there is a problem in thatthe antenna is broken or a discharge occurs in a gas passage between thedielectric material separation wall and the dielectric material showerplate.

DISCLOSURE OF INVENTION

It is a general object of the present invention to provide an improvedand useful plasma processing apparatus in which the above-mentionedproblems are eliminated.

A more specific object of the present invention is to provide a plasmaprocessing apparatus which can generate a plasma having high stabilityeven if any process gas is used since there is no film deposition due todissociation and combination of the process gas on a surface of adielectric material shower plate of a microwave introducing part.

It is another object of the present invention to provide a plasmaprocessing apparatus of which chamber cleaning period or a maintenanceperiod is long.

It is a further object of the present invention to provide a plasmaprocessing apparatus which can deal with a process in which ahigh-ion-energy must be incident on a substrate surface.

Additionally, it is another object of the present invention to provide aplasma processing apparatus which can perform an excellent filmdeposition process or etching process due to an appropriate control ofdissociation of the process gas, and can achieve a high plasmaexcitation efficiency.

In order to achieve the above-mentioned objects, a new process gasdischarge unit (referred to as a lattice-like shower plate) is providedto a plasma diffusion part (between a dielectric material shower plateand a substrate) of the conventional microwave plasma processingapparatus so that the plasma excitation gas mainly containing an inertgas and the process gas can be discharged from different locations.Additionally, by grounding the metal made lattice-like shower plate, theapparatus can deal with a process in which high-energy ions must beincident on a surface of the substrate which process cannot be performedby a conventional microwave plasma processing apparatus. Further, athickness of a dielectric material part of a microwave introducing partis optimized so as to maximize an efficiency of plasma excitation, and,at the same time, a thickness of the dielectric material shower plateand a distance between a slot antenna and a dielectric materialseparation wall are optimized so as to be capable of supplying amicrowave having a large power.

The plasma processing apparatus of the present invention has a structurein which the new gas discharging means (lattice-like shower plate) isprovided between the dielectric material shower plate of theconventional microwave plasma processing apparatus and a substrate, anda process gas of which dissociation is preferably suppressed isdischarged toward the substrate. On the other hand, in order to preventthe process gas from diffusing toward the dielectric material showerplate, the plasma excitation gas mainly containing an inert gas isdischarged from the dielectric material shower plate which is located onopposite side of the lattice-like shower plate with respect to thesubstrate. Since a film is not deposited on a surface of the dielectricmaterial shower plate which is a path of the microwave, a chambercleaning period or a maintenance period can be increased, and a stableplasma can be always obtained. Additionally, since a state in which aprocess gas rarely present can be formed near a surface on which amicrowave having a high plasma density and a high electron temperatureis incident, the dissociation of the process gas is suppressed and ahigh-performance process can be achieved. At the same time, since stableplasma having a high density sufficiently greater than a cutoff densitycan be excited near a surface on which the microwave is incident even ifa large amount of process gas is discharged from the lattice-like showerplate, a freedom of the process is greatly improved, and a higher-speedprocess can be achieved.

An area of the grounded part to which the plasma contacts is greatlyincreased by introducing the grounded metal made lattice-like showerplate into the plasma.

When a RF bias is applied to the substrate, a large part of the RFvoltage can be applied to a sheath near the substrate, and, thereby, theenergy of ions incident on the surface of the substrate can beefficiently increased without increasing a potential of the plasma.Accordingly, the present invention can be effectively applied to aprocess such as a reactive ion etching in which a high ion-energy mustbe incident on a surface of a substrate.

Additionally, according to the plasma processing apparatus of thepresent invention, an efficiency of excitation of the plasma ismaximized by optimizing a thickness of the dielectric material part ofthe microwave introducing part (a thickness of the dielectric materialseparation wall plus a thickness of the dielectric material showerplate), and, at the same time, a microwave having a large power can besupplied by optimizing a thickness of the dielectric material showerplate and a distance between the slot antenna and the dielectricmaterial separation wall, and, thereby a more stable and high-densityplasma can be efficiently produced. The metal-made lattice-like showerplate is constituted by a stainless steel and aluminum having analuminum oxide film which has an excellent resistance to the plasma of acorrosive gas, and is usable for a long time.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a microwave plasma processingapparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view of a lattice-like shower plate shown in FIG. 1viewed from a side of a substrate.

FIG. 3 is a graph showing a distribution of plasma potential in a plasmaspace.

FIG. 4 is a graph showing a variation in an electron density withrespect to time when deposition of tantalum is performed.

FIG. 5 is a graph showing a dependency of a RF electric power applied toa substrate with respect to ion energy incident on the surface of thesubstrate.

FIG. 6 is a graph showing a dependency of ion energy incident on asurface of a grounded part with respect to ion energy incident on thesurface of the substrate.

FIG. 7 is a graph showing a dependency of an electron density withrespect to a thickness of a dielectric material part.

FIG. 8 is a graph showing a dependency of a microwave electric powerdensity at which an electric discharge begins in a gap with respect to athickness of a dielectric material shower plate.

FIG. 9 is a graph showing a dependency of a microwave electric powerdensity at which an electric discharge begins in a process space withrespect to an interval between a dielectric material shower plate and alattice-like shower plate.

FIG. 10 is a graph showing a dependency of a microwave electric powerdensity at which an electric discharge begins in a slot part withrespect to an interval between a radial line slot antenna and adielectric material shower plate.

FIG. 11 is a plan view of a lattice-like shower plate, which is formedof a porous ceramic, provided in a microwave plasma processing apparatusaccording to a second embodiment of the present invention viewed from aside of a substrate.

FIG. 12 is a cross-sectional view taken along a line XII-XII of FIG. 11.

FIG. 13 is a plan view of a lattice-like shower plate, which is formedof aluminum, provided in a microwave plasma processing apparatusaccording to a third embodiment of the present invention viewed from aside of a substrate.

FIG. 14 is a cross-sectional view taken along a line XIV-XIV of FIG. 13.

FIG. 15 a cross-sectional view of a plasma processing apparatusaccording to a fourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will now be given, with reference to the drawings, ofplasma processing apparatuses according to embodiments, of the presentinvention, but, the present invention is not limited to the embodiments.

Embodiment 1

FIG. 1 is a cross-sectional view of a plasma processing apparatusaccording to a first embodiment of the present invention. The plasmaprocessing apparatus according to the first embodiment of the presentinvention comprises a vacuum chamber 101, a dielectric materialseparation wall 102, a dielectric material shower plate 103, a gap 104,a plasma excitation gas supply port 105, a plasma excitation gasintroducing passage 106, plasma excitation gas discharge holes 107,O-rings 108 and 109, a radial line slot antenna 110, a lattice-likeshower plate 111, process gas supply ports 112, process gas dischargeholes 113, a stage 115 and exhaust ports 116. A substrate 114 to beprocessed by plasma is placed on the stage 115.

In the present embodiment, the vacuum chamber 101 is formed of aluminum,and the dielectric material separation wall 102 and the dielectricmaterial shower plate 103 are formed of aluminum nitride having arelative permittivity of 8.63. A frequency of a microwave for plasmaexcitation is 2.45 GHz. The substrate 114 is a silicon substrate havinga diameter of 200 mm.

A microwave emitted by the radial line slot antenna 110 located in anatmosphere is introduced into an interior of the vacuum chamber 101 bybeing passed through the dielectric material separation wall 102, thegap 104 and the dielectric material shower plate 103, and generatesplasma by ionizing a gas in the vacuum chamber 101.

The apparatus has a structure in which a plasma excitation gas and aprocess gas can be discharged from different shower plates. The plasmaexcitation gas is supplied from the plasma excitation gas supply port105, and is lead to the center of the dielectric material shower plate103 by being passed through the plasma excitation gas introducingpassage 106. Thereafter, the plasma excitation gas flows in the gap in aradial direction from the center to the periphery, and is dischargedfrom the plurality of plasma excitation holes 107 to the interior of thevacuum chamber. On the other hand, the process gas is supplied to theprocess gas supply ports 112, and is passed through an interior of thelattice-like shower plate 11 which is constituted by a metal pipe, andis discharged from the plurality of process gas discharge holes 113 tothe side of the substrate 114.

FIG. 2 is a plan view of the lattice-like shower plate 111 viewed fromthe side of the substrate 114. The lattice-like shower plate 111comprises a main pipe 201, branch pipes 202, the process gas dischargeholes 113 and lattice-like shower plate gas supply ports 204. A circle205 indicated by a dashed line is an area facing the substrate 114. Inthe present embodiment, two lattice-like shower plate gas supply ports204 are provided so as to evenly discharge the gas onto the substrate114. The main pipe 201 and the branch pipes 202 are metal pipes havingother diameter of 9.53 mm (⅜ inches) and 6.35 mm (¼ inches),respectively, and connection parts therebetween are welded. The branchpipes 202 are positioned in a lattice arrangement, and openings 206 areformed between the main pipe 201 and the branch pipes 202. The branchpipes 202 are provided with many gas discharge holes 113 at positions atwhich the process gas is obliquely incident on the surface of thesubstrate evenly over the entire surface of the substrate. In thepresent embodiment, although the process gas is obliquely incident onthe surface of the substrate so as to improve substrate in-planeuniformity of a process, the process gas may be vertically incident onthe surface of the substrate.

In the present embodiment, a high-density aluminum containing stainlesssteel, which contains a larger amount of an aluminum component (4.16%)than that of the conventionally used stainless steel SUS316L, is usedfor the material of the pipes, and the pipes are treated at a hightemperature (900° C.) in a low oxidization atmosphere so as to form analuminum oxide passivation film, which is extremely thermodynamicallystable, on the surfaces of the pipes so that the pipes can besemi-permanently used eave in a corrosive gas plasma atmosphere. It hasbeen found that the formation of the aluminum oxide passivation filmprovides an excellent corrosion resistance with respect to plasma of acorrosive gas such as chlorine gas or fluorine gas

The radial line slot antenna 110, the dielectric material separationwall 102, the dielectric material shower plate 103, the lattice-likeshower plate 111 and the substrate 114 are positioned parallel to eachother. A distance between the dielectric material shower plate 103 andthe lattice-like shower plated 111 is set to a quarter (30 mm) of awavelength of the microwave in a vacuum; a distance between the surfaceof the dielectric material separation wall 102 facing the antenna 110and the surface of the dielectric material shower plate 103 facing thesubstrate 114 is set to three quarters (30.7 mm including the gap 104 of0.7 mm) of a wavelength of the microwave in the corresponding part; athickness of the dielectric material shower plate 103 is set to a half(20 mm) of a wavelength of the microwave in the corresponding part.Further, a distance between the radial line slot antenna 110 and thedielectric material separation wall 102 is set to a quarter (30 mm) of awavelength of the microwave.

If the lattice-like shower plate 111 shown in FIG. 2 is situated in thechamber, a contamination may occur since the material of the showerplate is sputtered by bombardment of ions from the plasma onto a surfaceof the shower plate and the sputtered material enters near the surfaceof the substrate. A sheath is formed near a surface of an objectinserted into plasma, and ions in the plasma are accelerated by theelectric field in the sheath and incident on the surface of the object.If the energy of the incident ions is equal to or greater than athreshold value peculiar to the material or the ions, a sputteringoccurs, but if less than the threshold value, no sputtering occurs. Forexample, when Ar⁺ ions are incident on a surface of various metals, thethreshold value is about 10 eV to 30 eV. In order to prevent acontamination due to sputtering, the energy of ions incident on thelattice-like shower plate 111 is preferably reduced to about 10 eV.

The energy (eV) of the ions incident on a surface of a grounded part inplasma is almost equal to a voltage eVp, where Vp is a plasma potentialand e is a charge of an electron. Also if the surface of the groundedobject is covered by an insulating film, the energy is almost the samevalue. FIG. 3 is a graph showing a distribution of a plasma potential ina plasma space. In FIG. 3, a01 indicates a result obtained by themicrowave plasma processing apparatus shown in FIG. 1, and a02 indicatesa result obtained by an RF excitation parallel plate type plasmaprocessing apparatus. A distance of the plasma space was 120 mm, the gaswas Ar and a pressure was about 67 Pa for both cases. In FIG. 3, thehorizontal axis Z represents a position in the plasma space in adirection vertical to the substrate, and a surface of the dielectricmaterial shower plate 103 was set as a reference in the microwave plasmaprocessing apparatus and the surface of the RF applying electrode wasset as a reference in the parallel flat plate type plasma processingapparatus. It should be noted that a 2.45 GHz microwave was introducedby being passed through the dielectric material shower plate 103, and a3.56 MHz RF wave was applied to the RF applying electrode so as togenerate plasma.

In the parallel plate type plasma processing apparatus, the plasmapotential is about 33 V, and it is apparent a contamination occurs dueto sputtering if the lattice-like shower plate 111 is situated in thechamber. On the other hand, in the microwave plasma processingapparatus, since the plasma potential is less than 8 V at a positionaway from the dielectric material shower plate 103 by a distance morethan 20 mm, there is no possibility of sputtering even if thelattice-like shower plate 111 is situated in the plasma. Although thereare inductively coupled plasma apparatus and an electron cyclotronresonance plasma apparatus as other plasma apparatuses used for asemiconductor manufacturing process, the plasma potential is higher than30 V in any apparatus. As mentioned above, the microwave plasmaapparatus has a feature that the plasma potential is extremely low ascompared to other plasma apparatuses. This is caused by an electrontemperature being controlled low over entire plasma including a plasmaexcitation part. Such an effect can be firstly provided withoutoccurrence of contamination due to sputtering by combining thelattice-like shower plate 111 and the microwave plasma apparatus.

Experiments were performed for forming a tantalum thin film on a 200 mmdiameter silicon substrate covered by a silicon oxide film according toa plasma CVD (chemical vapor deposition) method. FIG. 4 shows a resultof measurement of variations of an electron density in the plasma withrespect to passage of deposition time after start of deposition of atantalum film in a state in which deposited materials on a surface ofthe dielectric material shower plate 103 is completely removed. A curve301 indicates a result of a conventional microwave plasma apparatusstructure, that is, in a case in which the plasma excitation gas and theprocess gas are mixed and discharged together from the dielectricmaterial shower plate 103 without providing the lattice-like showerplate 111. A curve 302 indicates a result of the microwave plasmaapparatus structure according to the present invention, that is, in acase in which the plasma excitation gas and the process gas areseparately discharged by providing the lattice-like shower plate 111.

The measurement of the electron density was performed at a position awayfrom a wafer by 15 mm along a center axis of the wafer. As for theprocess gas, a gas produced by bubbling Ar carrier gas in liquefiedTa(O—C₂H₅)5 was used. As for the plasma excitation gas, Ar was used.Flow rate of the process gas and the plasma excitation gas ware 150 sccmand 500 sccm, respectively, and the pressure in the vacuum chamber wasabout 80 Pa (0.6 Torr). A frequency of the microwave for plasmaexcitation was 2.45 GHz, and a power thereof was 1.1 kW.

In the conventional structure, the electron density was graduallydecreased after a deposition time of 3 minutes has passed and the plasmabecame unstable, and finally the plasma disappeared when 11 minutes haspassed. This is because the tantalum film deposited on the surface ofthe dielectric material shower plate 103 reflected and absorbed themicrowave. As a result of accrual analysis of the film deposited on thesurface of the dielectric material shower plate 103, it was found that atantalum film containing a large amount of carbon was deposited.

An average thickness of the tantalum film was 4.3 μm.

On the other hand, in the structure according to the present invention,the electron density did not change even if the deposition was performedfor 20 minutes, and deposition of the tantalum film on the surface ofthe dielectric material shower plate 103 was not found. The reason forthe electron density being slightly lower than that of the conventionalstructure immediately after a start of deposition is that the plasma isslightly prevented from diffusing to a periphery of the wafer due to thepresence of the lattice-like shower plate 111. In the conventionalstructure, since the tantalum film was deposited on the surface of theshower plate during film deposition, cleaning of an inner surface andmaintenance of the chamber using chlorine gas plasma or the like must befrequently performed after film deposition, which was uneconomical andreduced a throughput. However, in the structure of the presentinvention, very little cleaning and maintenance were needed, whichresulted in a remarkable improvement in the throughput.

A description will now be given of a result of evaluation on acharacteristic of the tantalum thin film formed on the silicon oxidationfilm. When an amount of carbon contained in the tantalum thin film wasmeasured by a secondary ion mass spectrograph, the amount of carbonaccording to the conventional structure was as large as 10.5%, while theamount of carbon according to the structure of the present invention was0.3%. In the conventional structure, since the organic metal gas wasdischarged from the dielectric material shower plate 103, the gasmolecules were decomposed in excess by plasma having a high density anda relatively high temperature in the vicinity of a surface on which theplasma is incident, and organic materials having a small molecularweight were produced and the organic materials were incorporated intothe film. However, in the structure of the present embodiment, since theorganic metal gas was discharged from the lattice-like shower plate 111to a plasma diffusion area in which an electron temperature was low, thecoupling between the tantalum atom and the organic molecule wasselectively cutoff, and, thereby, only organic materials having a highvapor pressure were produced.

Further, when an electric resistivity of the tantalum thin film, theresistivity was 225×10⁻⁶ Ωcm due to a large amount of carbon containedtherein in the conventional structure, while the resistivity was 21×10⁻⁶Ωcm which was lower more a single digit lower than that of theconventional structure, and it was found that an almost ideal thin filmwas formed. As mentioned above, the characteristic of the thin film canbe greatly improved by applying the plasma processing apparatusaccording to the present invention to a CVD process of a metal thinfilm, a feroelectric thin film or a high permittivity thin film.

A description will now be given of compatibility of the microwave plasmaapparatus to an etching process. FIG. 5 is a graph showing how much RFpower must be applied to the substrate so as to obtain energy of ionsincident on the surface of the substrate necessary for etching. A curve401 indicates a result of the structure of the conventional microwaveplasma apparatus, that is, a case in which the grounded lattice-likeshower plate 111 is not present, and a curve 401 indicates a result ofthe structure of the microwave plasma apparatus according to the presentinvention, that is, a case in which the grounded lattice-like showerplate 111 is present. As for the plasma excitation gas, Ar was used. Apressure in the vacuum chamber was about 4 Pa (30 mTorr), a frequency ofthe microwave for plasma excitation was 2.45 GHz, and an electric powerwas 1.1 kW. Additionally, a frequency of the RF applied to the substratewas 2 MHz.

According to FIG. 5, it can be interpreted that according to thestructure of the present invention it is sufficient to apply about onefifth of the RF power of the conventional structure so as to obtain anenergy of ions incident on a surface of the same substrate. That is, aremarkable increase in an efficiency and miniaturization and costreduction of an RF power source and a matching unit can be achieved.

FIG. 6 is a graph showing a variation in the energy of ions incident ona surface of a grounded part when a power necessary for obtaining theenergy of ions incident on the surface of the substrate for etching isapplied to the substrate. A curve 501 indicates a result of thestructure of the conventional microwave plasma apparatus structure, thatis, a case in which the grounded lattice-like shower plate 111 is notpresent, and a curve 501 indicates a result of the structure of themicrowave plasma apparatus according to the present invention, that is,a case in which the grounded lattice-like shower plate 111 is present.Other conditions are the same as the case of FIG. 5.

It can be appreciated from FIG. 6 that, in the conventional structure,the energy of ions incident on the surface of the grounded part is avery high value as high as the energy of ions incident on the surface ofthe substrate. For example, in a reactive ion etching of a silicon oxidefilm, ions having about 400 eV must be incident on the surface of thesubstrate. In order to obtain the energy of incident ions, an RFelectric power of 1600 W must be applied to the substrate, and, thereby,the energy of ions incident on the surface of the grounded part becomes370 eV. If ions having such a high energy of movement are incident onthe surface of the grounded part of the chamber wall or the lattice-likeshower plate, the wall surface is sputtered which causes an impuritycontamination. Additionally, since the wall surface is removed bysputtering, a service life is extremely shortened. On the other hand, inthe structure of the present invention, since the area of the surface ofthe grounded part to which the plasma contacts is sufficiently largerthat the area of the substrate, the energy of ions incident on thesurface of the grounded part is reduced to a low value ranging from 10eV to 20 eV, and, thus, the surface of the grounded part is not subjectto sputtering.

Table 1 shows: an etching selectivity of a resist to a silicon oxidefilm when etching is performed on the silicon oxide film on a surface ofa silicon substrate; an etching selectivity of a silicon nitride film toa silicon oxidation film which is indispensable for forming aself-aligning contact; and a result of measurement of a contactresistance between an underlying silicon and an aluminum electrode whichis formed after forming a 0.25 μm contact hole having a silicon oxidefilm.

TABLE 1 Comparison of etching characteristics when etching is performedby a conventional apparatus and the apparatus according to the presentinvention. Using Using apparatus of conventional the present apparatusinvention Etching selectivity of a 4.8 10.9 resist to a silicon oxidefilm Etching selectivity of a 18 38 silicon nitride film to a siliconoxide film Contact resistance for a 3.7 Ω 0.48 Ω contact diameter of0.25 μm

As for the plasma excitation gas, Ar was used. The flow rate of theplasma excitation gas was 320 sccm. Additionally, as for the processgas, a mixture gas of C₄F₈/CO/O₂/Xe was used. The flow rate of theprocess gas was 105 sccm. The pressure in the vacuum chamber was about 4Pa (30 mTorr). The frequency of the RF wave applied to the surface ofthe substrate was 2 MHz. The power of the RF wave applied to thesubstrate was set so that the energy of ions incident on the surface ofthe substrate becomes 400 eV.

In order to realize a next generation ultra fine high-performancesemiconductor device, the selectivity between a resist and a siliconoxide film must be equal to or greater than 10, and the selectivitybetween a silicon nitride film and a silicon oxide film must be equal toor greater than 30. In the conventional structure, a sufficient etchingselectivity cannot be obtained with respect to both the resist and thesilicon nitride film since decomposition of fluorocarbon gas progressesin excess which generates a large amount fluorine radicals or fluorineions causing a decrease in the selectivity. Additionally, since thesurface of the grounded part such as a chamber wall is subjected tosputtering and sputtered material enter a silicon surface on the bottomof the contact hole, a contact resistance becomes very high.

Since it cannot be used for a device as it is, there is needed a processof removing a damaged layer in the vicinity of the surface of thesilicon, which causes an increase in a semiconductor manufacturing costand a decrease in the productivity.

On the other hand, according to the structure of the present invention,since the process gas is introduced into a portion of the plasmadiffusion part in an electron temperature is extremely low,decomposition of fluorocarbon gas is appropriately suppressed, and asufficient etching selection ratio can be obtained for both the resistand the silicon nitride film. Additionally, since there is no impuritycontamination, the contact resistance is controlled to be small.

FIG. 7 is a graph showing a result of measurement of variations of anelectron density in plasma when the thickness of the dielectric materialpart (the thickness of the dielectric material separation wall 102+thethickness of the dielectric material shower plate 103) is changed whilea supplied microwave power is maintained constant. The frequency of themicrowave was 2.45 GHz, and the microwave power was 1.8 kW. The gap 104was 0.7 mm. The gas was Ar, and a pressure thereof was 67 Pa (500mTorr). The electron density was measured at a point away from thedielectric material shower plate by 22 mm.

It was found from FIG. 7 that the electron density in the plasma variesperiodically with the thickness of the dielectric material part. Theefficiency of plasma excitation (a power used for plasma excitation/apower supplied by the microwave power source) is proportional to theelectron density. In the present embodiment, the efficiency of plasmaexcitation periodically varied in a range from 21% to 75% with thevariation in the thickness of the dielectric material part. Thisphenomenon can be explained as follows.

The electron density (higher than 10¹² cm⁻³) near the surface on whichthe microwave is incident is sufficiently higher than a cutoff density(45×10¹⁰ cm⁻³), the microwave incident on the plasma surface cannotenter the plasma deeper than an entering length (about 3 mm) from thesurface of the plasma. The reflected microwave is received by theantenna, and, thereafter, reflected by the matching unit and emittedfrom the antenna. That is, a space between the plasma surface and thematching unit is in a resonant state. In this space, a microwave havinga high-energy density is present, and, thereby, a large loss isgenerated due to a small conductor loss or a small dielectric loss ofthe dielectric material in the slot antenna. If the loss is larger thana power supplied from the microwave to the plasma, the power density ofthe microwave between the plasma surface and the matching unit rarelydepends on a state of the plasma. On the assumption that the powerdensity of the microwave in the resonator is constant, the power densityof the microwave in the dielectric material part is maximized when thethickness of the dielectric material part is such that the surfacethereof facing the antenna is at a position corresponding to a loop ofthe standing wave of the microwave electric field, and the plasma can bemost effectively excited. On the contrary, the power density of themicrowave in the dielectric material part is minimized when thethickness of the dielectric material part is such that the surfacethereof facing the antenna is at a position corresponding to a node ofthe standing wave of the microwave electric field, and the efficiency ofplasma excitation becomes lowest. In order to locate the surface of thedielectric material part facing the antenna at a position of the loop ofthe standing wave of the microwave electric field, a distance betweenthe surface of the dielectric material separation wall facing theantenna and the surface of the dielectric material shower plate facingthe substrate is set equal to an odd multiple of a quarter of thewavelength in the corresponding part. This is because the surface of thedielectric material shower plate 103 facing the substrate can beregarded as a short-circuit plane (position of a node of the standingwave) due to the presence of the plasma which can be regarded as aconductor. It can be appreciated from FIG. 7 that the thickness of thedielectric material part at which the electron density takes a maximumvalue is 30 mm and 50 mm. These values correspond to the distancebetween the surface of the dielectric material separation wall facingthe antenna and the surface of the dielectric material shower platefacing the substrate being three quarters and five quarters of thewavelength, respectively.

In the conventional structure, since the thickness of the dielectricmaterial part is determined based on only a mechanical strength thereof,there are many cases in which the efficiency of plasma excitation islow, and the efficiency varies for each apparatus. In the structure ofthe present invention, the efficiency of plasma excitation is as high as75%, and reaches 3.6 times that of the conventional structure at amaximum. That is, high-density plasma can be generated by a small,inexpensive microwave power source with less power consumption.

FIG. 8 is a graph showing a result of measurement of a power density ofthe microwave at which a discharge begins in the gap 104 when thethickness of the dielectric material shower plate 103 is varied whilethe thickness of the dielectric material part is fixed to 30 mm. It canbe appreciated that the power density of the microwave at which adischarge begins in the gap periodically varies with the thickness ofthe dielectric material shower plate 103. If a discharge occurs in thegap, the plasma in the process space becomes unstable, and, thus, such adischarge must be positively prevented. In order to prevent thedischarge, the thickness of the dielectric material shower plate 103 isdetermined so that the gap is located at a position of a node of thestanding wave of the microwave electric field. That is, the thickness ofthe dielectric material shower plate can be an integral multiple of ahalf of the wavelength in the corresponding part. It can be appreciatedfrom FIG. 8 that a discharge most hardly occurs when the thickness ofthe dielectric material shower plate 103 is 20 mm, and most easilyoccurs when the thickness is 10 mm. These values correspond to a halfand a quarter of the wavelength, respectively.

In the conventional structure, since the thickness of the shower platewas determined based on only a mechanical strength thereof and aconductance of the gas, there were many cases in which a dischargeoccurs in the gap and, thus, it was difficult to supply a large power tothe plasma. In the structure of the present invention, no dischargeoccurs in the gap 104 when a large power is supplied to the plasma, and,thereby, it is possible to continuously excite stable, high-densityplasma.

FIG. 9 is a graph showing a result of measurement of an electron densityhear the substrate 114 and a power density of the microwave at which adischarge begins in the process space (between the dielectric materialshower plate 103 and the substrate 114) when a distance between thedielectric material shower plate 103 and the substrate 114 is varied.

When the distance between the dielectric material shower plate 103 andthe substrate 114 becomes larger than a quarter of the wavelength, adischarge abruptly becomes to be difficult to occur in the processspace. This can be explained as follows. The lattice-like shower plate111 constituted by a metal serves a short-circuit plane for themicrowave if the lattice interval is sufficiently shorter than thewavelength of the microwave. After the microwave is supplied to thechamber, the wave incident on the lattice-like shower plate 111 and thereflected wave reflected near the surface of the lattice-like showerplate 111 together form a standing wave. If the distance between thedielectric material shower plate 103 and the lattice-like shower plate111 is longer than a quarter of the wavelength, a loop of the standingwave of the microwave electric field is present in the plasma space, anda discharge begins at a position where the electric field is strong.

Immediately after the discharge begins, high-density plasma is generatednear the surface on which the microwave is incident by using the plasmaas a seed. On the other hand, if the distance between the dielectricmaterial shower plate 103 and the lattice-like shower plate 111 isshorter than a quarter of the wavelength, the microwave electric fieldis maximized in the surface of the dielectric material shower plate 103,but the intensity of the electric field decreases as the distancedecreases, which results in less discharge.

It can be interpreted from FIG. 9 that the electron density hear thesubstrate decreases as the distance between the dielectric materialshower plate 103 and the lattice-like shower plate 111 increases. Thisis because the electron density decreases as the distance from thesurface on which the microwave is incident increases since the plasma isexcited near the surface on which the microwave is incident and theplasma diffuses toward the substrate. In order to achieve a high-speedprocess at a low microwave power, it is preferable that a dischargeeasily occurs in the process space and the electron density near thesubstrate is high. In order to satisfy both requirements, it ispreferable to set the distance between the dielectric material showerplate 103 and the lattice-like shower plate 111 to be equal to a quarterof the wavelength.

FIG. 10 is a graph showing a result of measurement of a power density ofthe microwave at which a discharge begins in the slot part of theantenna 110 when the distance between the radial line slot antenna 110and the dielectric material shower plate 103 is varied while thethickness of the dielectric material part is fixed to 30 mm. It can beappreciated that the power density of the microwave at which a dischargebegins in the slot part periodically varies with the distance betweenthe radial line slot antenna 110 and the dielectric material showerplate 103. If a discharge occurs in the slot part, the antenna 110 isdamaged, and the plasma in the process space becomes unstable, and,thus, such a discharge must be positively prevented. In order to preventthe discharge in the slot part, the distance between the antenna 111 andthe dielectric material shower plate 103 is determined so that thesurface of the antenna 110 is located at a position of a node of thestanding wave of the microwave electric field. When the surface of thedielectric material shower plate 103 facing the antenna corresponds to aloop of the standing wave of the microwave electric field, that is, in acase in which the surface of the dielectric material separation wallfacing the antenna and the surface of the dielectric material showerplate 103 facing substrate is set equal to an odd multiple of a quarterof the wavelength in the corresponding part, the distance between theantenna 110 and the dielectric material shower plate 103 can be an oddmultiple of a quarter of the wavelength. It can be appreciated from FIG.10 that a discharge most hardly occurs when the distance between theantenna 110 and the dielectric material shower plate 103 is 30 mm and 90mm, and most easily occurs when the distance is 60 mm. These valuescorrespond to a quarter, two quarters and three quarters of thewavelength, respectively.

In the conventional structure, since there were many cases in which adischarge easily occurs in the slot part of the antenna 110 and, thus,it was difficult to supply a large power to the plasma. In the structureof the present invention, no discharge occurs in the slot part when alarge power is supplied to the plasma, and, thereby, it is possible tocontinuously excite stable, high-density plasma.

As mentioned above, by using the apparatus according to the presentinvention, it can be achieved to apply a high-efficiency RF bias to asubstrate and to generate a high-efficiency microwave plasma, andattempts can be made to reduce an area occupied by the apparatus byminiaturization of an RF power source or a microwave power source and toreduce a cost of the apparatus. Further, since there is no dischargeoccurs in the gap between the dielectric material separation wall andthe dielectric material shower plate 103 or the slot part of the radialline slot antenna 110 even when a microwave having a large power issupplied, more high-density and stable plasma can be generated, whichrealizes a high-productivity process. Since excessive dissociation ofthe process gas is suppressed and there is no impurity contamination, ahigh-performance process, which innovates the conventional plasmaprocess, can be achieved.

Embodiment 2

A description will now be given, with reference to FIG. 11 and FIG. 12,of a plasma processing apparatus according to a second embodiment of thepresent invention. FIG. 11 is a plan view of a lattice-like shower plate600 provided in the plasma processing apparatus according to the secondembodiment of the present invention viewed from a side of a substrate.FIG. 12 is a cross-sectional view taken along a line XII-XII of FIG. 11.The plasma processing apparatus according to the second embodiment ofthe present invention is the same as the plasma processing apparatusaccording to the first embodiment of the present invention shown in FIG.1 except for the lattice-like shower plate 600 shown in FIG. 11, anddescriptions thereof will be omitted.

As shown in FIG. 11, the lattice-like shower plate 600 comprises a mainpipe 601, branch pipes 602, process gas discharge parts 603 (hatchedportions) and lattice-like shower plate gas supply ports 604. As shownin FIG. 12, each of the branch pipes 602 has a film 606. It should benoted that a circle 605 indicated by a dotted line indicates an areafacing the substrate.

In the present embodiment, the main pipe 601 is formed of an aluminaceramic having a porosity of 0.03%, and the branch pipes 602 are formedof a porous alumina ceramic having a porosity of 32%. The branch pipes602 are positioned in a lattice arrangement, and the main pipe 601 andthe branch pipes 602 are joined to each other by a ceramic-typeadhesive. Accordingly, openings 607 are formed by the main pipe 601 andthe branch pipes 602. The porous alumina ceramic has a nature totransmit gas therethrough, and, thus, a pipe made of such a materialserves as a shower plate by setting a pressure of inside the pipeappropriately higher than a pressure outside the pipe. If the porousalumina ceramic is used for a shower plate, gas can be discharged moreevenly than a case in which many gas discharge holes are provided as inthe above-mentioned first embodiment. Parts of the surfaces of branchpipes 602 other than the gas discharge parts are covered by the film 606so as to prevent gas from being discharged therethrough. The film 606 ismade of an alumina ceramic having a thickness of 220 μm and a porosityof 0.8%.

The alumina ceramic has an excellent durability with respect tocorrosive gas plasma, and a shower plate having a long service life canbe constituted. On the other hand, since the alumina ceramic does nothave an electric conductivity, there is no effect to increase an area ofa grounded surface to which the plasma contacts, and, thus, it is notsuitable for a process such as a reactive ion etching or the like inwhich a high-energy ions must be incident on the surface of thesubstrate. Accordingly, the apparatus according to the presentembodiment is preferably used for resist ashing or film deposition suchas CVD, oxidation or nitriding.

In the present embodiment, although the lattice-like shower plate 600 isformed of an alumina ceramic, the shower plate 600 may be formed of analuminum nitride ceramic having a high thermal conductivity.Alternatively, a conductive alumina ceramic containing a large amount ofmetal such as aluminum or stainless steel. In such a case, since thereis an effect of increasing the area of the grounded surface to which theplasma contacts, the shower plate is applicable to a process in whichhigh-energy ions must be incident on the surface of the substrate.

Embodiment 3

A description will now be given, with reference to FIG. 13 and FIG. 14,of a plasma processing apparatus according to a third embodiment of thepresent invention. FIG. 13 is a plan view of a lattice-like shower plate700 provided in the plasma processing apparatus according to the thirdembodiment of the present invention viewed from a side of a substrate.FIG. 14 is a cross-sectional view taken along a line XIV-XIV of FIG. 13.The plasma processing apparatus according to the third embodiment of thepresent invention is the same as the plasma processing apparatusaccording to the first embodiment of the present invention shown in FIG.1 except for the lattice-like shower plate 700 shown in FIG. 13, anddescriptions thereof will be omitted.

The lattice-like shower plate 700 shown in FIG. 13 comprises gasintroducing passages 701, process gas discharging holes 702,lattice-like shower plate gas supply ports 703, a lattice-like showerplate body 705 and a lattice-like shower plate cover 706. It should benoted that a circle 704 indicated by a dotted line indicates an areacorresponding to a substrate.

The gas introducing passages 701 having a square cross section areformed in a grid, and the opening 707 is formed between adjacent gasintroducing passages so as to let plasma and gas pass therethrough. Thelattice-like shower plate body 705 and the lattice-like shower platecover 706 are formed of aluminum containing 3%-magnesium, and are joinedto each other by electron beam welding. The lattice-like shower platebody 705 and the lattice-like shower plate cover 706 are subjected to aheat treatment within a fluorine gas atmosphere after the electron beamwelding so as to improve a resistance with respect to a corrosive gas,and a mixture film of magnesium fluoride and aluminum fluoride is formedthereon.

Since the present embodiment uses a material having a small resistivityand a large cross-sectional area of paths through which the RF currentof the lattice-like shower plate 700 flows, as compared to theabove-mentioned first embodiment, the effect to reduce an impedancebetween the plasma and the ground is high. That is, a plasma apparatushaving a higher power efficiency can be constituted. It should be notedthat, in the present embodiment, although the lattice-like shower plate700 is formed of aluminum, the shower plate may be formed of a stainlesssteel or a high-purity aluminum containing stainless steel.

Embodiment 4

FIG. 15 is a cross-sectional view of a plasma processing apparatusaccording to a fourth embodiment of the present invention. The plasmaprocessing apparatus according to the fourth embodiment of the presentinvention comprises a vacuum chamber 801, a dielectric materialseparation wall 802, dielectric material shower plates 803, a gap 804, ashower plate fixing jig 805, plasma excitation gas supply ports 806,plasma excitation gas discharge holes 807, microwave guides 808, alattice-like shower plate 809, process gas supply ports 810, process gasdischarge holes 811, a stage 813 and an exhaust port 814. A substrate812 to be processed by plasma is placed on the stage 813.

In the present embodiment, the vacuum chamber is formed of aluminum; thedielectric material separation wall 802 is formed of aluminum oxide; thedielectric material shower plates 803 are formed of aluminum nitride;and the shower plate fixing jig 805 is formed of aluminum. Thelattice-like shower plate 809 has the same structure as that of one ofthe above-mentioned first to third embodiments, and is formed of ahigh-concentration aluminum containing stainless steel which is subjectto an oxidation passivation treatment, similar to the above-mentionedfirst embodiment. The frequency of the microwave for plasma excitationis 2.45 GHz. The substrate 812 is a square glass substrate for a liquidcrystal display, and its size is 550×650 mm².

Each of the microwave guides 808 is a single mode square waveguideextending in a direction perpendicular to the plane of the drawing, anda lower surface thereof is surrounded by a dielectric material wall andother parts are surrounded by meal walls. The microwave is generated bya single microwave power source, and is supplied by being distributed tothe two microwave guides 808 near the center portion of the apparatus. Apart of the microwave transmitting in the microwave guides 808 leaksfrom the dielectric material separation wall 802, and is introduced intothe vacuum chamber 801 via the dielectric material shower plate 803 soas to excite plasma. When the plasma is excited, a surface wave isexcited in the vicinity of a boundary between the plasma and thedielectric material shower plates 803 which surface wave propagatesalong the surface of the dielectric material shower plates 803. Uniformplasma over a large area can be obtained by exciting a uniform surfacewave. In the present embodiment, two dielectric material shower plates803 are provided, and these shower plates are electrically separatedfrom each other by the shower plate fixing jig 805 so as to prevent thesurface waves propagating the surfaces of these shower plates frominterfering with each other.

The dielectric shower plates 803, the lattice-like shower plate 809 andthe substrate 812 are arranged parallel to each other. A distancebetween each of the dielectric shower plates 803 and the lattice-likeshower plate 809 is set equal to a quarter (30 mm) of the wavelength ofthe microwave.

The plasma processing apparatus according to the present embodiment wasused for manufacturing a back gate type TFT (thin film transistor)liquid crystal display device. The applied processes were: 1) siliconnitride film forming process; 2) a polycrystalline silicon film formingprocess on a silicon nitride film; 3) an n⁺ silicon film forming processon a polycrystalline silicon film; 4) a silicon film etching process;and 5) a silicon surface direct oxidation process. The following Table 2indicates kinds of gasses and pressures used for the above-mentionedprocesses.

TABLE 2 Each process for manufacturing a liquid crystal display andprocess conditions thereof Plasma excitation Process gas Process gasPressure 1: Silicon nitride Ar S_(i)H₄ Approx. 67 Pa film forming (900sccm) (50 sccm) (500 mTorr) NH3 (70 sccm) 2: Polycrystalline Ar S_(i)H₄Approx. 67 Pa silicon film (880 sccm) (60 sccm) (500 mTorr) forming H2(60 sccm) 3: n⁺ silicon film Ar SiH₄ Approx. 67 Pa forming (900 sccm)(60 sccm) (500 mTorr) PH₃ (20 sccm) 4: Silicon film Ar SF₆ Approx. 27 Paetching (820 sccm) (250 sccm) (200 mTorr) HCl (50 sccm) 5: Siliconsurface He O₂ Approx. 67 Pa direct oxidizing (660 sccm) (90 sccm) (500mTorr)

Substrates of both semiconductors and liquid crystal displays have beenincreased in their sizes. It is technically difficult and takes a costto transport a large-size substrate at a high speed without anyproblems. Additionally, an apparatus has become large-scaled due to anincrease in the size of the substrate, and an initial investment and arunning cost of the apparatus or a manufacturing plant (clean room) hasbeen extremely increased. Accordingly, there is a great demand toconsecutively perform many processes by a single apparatus so as tocarry out manufacturing without transporting a substrate.

In the present embodiment, the processes 1) to 3) can be consecutivelyperformed without moving the substrate 812 by changing the gas. Theprocesses 4) and 5) are the same. The plasma processing apparatusaccording to the present embodiment can deal with such consecutiveprocesses in a flexible manner because of the feature that many plasmaprocesses such as film deposition, etching, oxidation, nitriding orashing can be performed by a single apparatus by changing gassesdischarged from the dielectric material shower plate 803 and thelattice-like shower plate 809.

The following Table 3 indicates a comparison of results of execution ofthe same process by a parallel flat plate type plasma processingapparatus (conventional apparatus), which is widely used in the recentmanufacturing of liquid crystal displays, and the plasma processingapparatus according to the present embodiment.

TABLE 3 Case of using Case of using conventional apparatus of theProcess apparatus present invention 1: Silicon nitride WithstandWithstand film forming voltage: 4.2 MV/cm voltage: 12.4 MV/cm Filmdeposition Film deposition rate: 120 nm/min rate: 310 nm/min 2:Polycrystalline Amorphous Polycrystal silicon film (0.2 cm²/V · sec)(0.2 cm²/V · sec) forming Film deposition Film deposition rate: 78nm/min rate: 93 nm/min 3: n⁺ silicon film Resistivity: Resistivity:forming 2.3Ω cm 0.7Ω cm Film deposition Film deposition rate: 58 nm/minrate: 85 nm/min 4: Silicon film Etching rate: Etching rate: etching 280nm/min 720 nm/min 5: Silicon surface Oxidation film Oxidation filmdirect oxidizing thickness: 7 nm thickness: 28 nm (oxidation time, 3(oxidation time, 3 min.) min.)

The silicon nitride film is used as a gate insulating film or aninterlayer insulating film, and is required to be deposited at a highrate in the form of a film having a high withstand voltage and a smallleak current. In the apparatus according to the present embodiment,since the energy of ions incident on the surface on which the film isdeposited is as low as one-third of that of the conventional apparatusand there is no damage to the thin film due to ion bombardment, ahigh-quality silicon nitride film is formed, which has a withstandvoltage close to three times that of the conventional one. Further,since the electron density is higher than the conventional parallel flatplate type plasma apparatus by about one order (>2×10¹² cm⁻³), a filmdeposition rate is high and productivity is remarkably increased.

The silicon film is used for a channel part, which is an important partof the TFT. A silicon film having a high channel moving speed must bedeposited on an insulating film so as to improve a current driveperformance of a transistor. In the conventional apparatus, the movingspeed was very low (0.2 cm²/V·sec) since it was able to form only anamorphous film.

Although a polycrystalline silicon film having a high moving speed canbe obtained by performing a laser annealing treatment whichpolycrystallizes an amorphous film by irradiating a laser beam, thismethod is not practical since it takes a very long time. When themicrowave plasma processing apparatus according to the present inventionis used, a polycrystalline silicon film having a high moving speed ofabout 280 cm²/V·sec was able to be deposited by a CAD method at a lowsubstrate temperature of 250° C. without annealing. Additionally, themicrowave plasma processing apparatus according to the present inventionis capable of depositing a film at a high rate and has an excellentproductivity, and provides an innovative thin film forming technology.

The n⁺ silicon film is used for a source-drain contact part of the TFT,and it is required to provided a high carrier density and a smallresistivity so as to improve a current drive performance of atransistor. When the apparatus according to the present invention wasused, there was no damage to a film since the energy of ions irradiatedto a surface on which a film is deposited is small, and it was able toobtain a film having a less resistivity due to an improvement in anactivation rate of carries.

The 4) silicon film etching process and 5) silicon direct oxidationprocess in Table 3 were consecutively performed by the same apparatuswithout taking the substrate 812 out of the apparatus. In theseprocesses, a gap between a source and a drain of the back gate type TFTwas etched, and, thereafter, the n⁺ silicon film (amorphous or microcrystal) for a source-drain contact of the substrate base was changedinto an insulating material (S_(i)O₂) by oxidation so as to insulatebetween the source and the drain. Although the etching must be performedat a high rate, an etching rate of more than twice as high as that ofthe conventional one was obtained due to a high plasma density when theapparatus according to the present invention was used.

In order to achieve an insulation between the source and the drain, theN⁺ silicon film (thickness of the film is about 15 mm) must becompletely oxidized up to the inside thereof. At this time, thetemperature of the substrate must be lower than 300° C. If alow-temperature plasma oxidation is performed by the conventionalapparatus, the oxidation progresses up to a depth of only about 7 mm.Accordingly, the film cannot be oxidized in its entirety, and aninsulation between the source and the drain cannot be achieved. On theother hand, according to the apparatus of the present embodiment, thesource and the drain can be completely insulated from each other byoxidizing the n⁺ silicon film in its entirety since the oxidationprogresses up to a depth of 28 mm at a substrate temperature of 300° C.for 3 minutes. This is because a large amount of oxygen radicals, whichare seeds of oxidation, are generated due to a high electron density,and diffusion of the oxygen radicals into the oxidation film is promotedby a large amount of ions irradiated onto the surface of the substrate.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

1-15. (canceled)
 16. A surface-wave microwave plasma processingapparatus for applying a process to a substrate to be processed, thesurface-wave microwave plasma processing apparatus comprising: a chamberof which interior can be depressurized; an exhaust gas system configuredand arranged to depressurize the chamber; an electrode provided in thechamber to hold the substrate to be processed; a flat plate dielectricmaterial plate configured and arranged to serve as a part of a wallforming the chamber; a flat plate slot antenna arranged above the flatplate dielectric material plate; a flat plate dielectric material showerplate provided adjacent to the flat plate dielectric material plate on aside opposite to the flat plate slot antenna, a gap being formed betweenthe flat plate dielectric material shower plate and the flat platedielectric material plate to cause a plasma excitation gas flowstherethrough, the flat plate dielectric material shower plate having agas discharge hole for introducing the plasma excitation gas into thechamber; and a metallic shower head arranged between the flat platedielectric shower plate and the electrode, the metallic shower headhaving a plurality of gas discharge openings for introducing a processgas into a plasma diffusion space, wherein a plasma excited by asurface-wave microwave flows into the plasma diffusion space by passingthrough the gas discharge openings.
 17. The surface-wave microwaveplasma processing apparatus as claimed in claim 16, wherein a distancebetween the flat plate dielectric shower plate and the metallic showerhead is substantially equal to or larger than a quarter of a wavelengthof the microwave in a vacuum.
 18. The surface-wave microwave plasmaprocessing apparatus as claimed in claim 17, wherein a surface of themetallic shower plate is covered by a corrosion resistant film.